[3.x] Backport Image.save_jpg and Image.save_jpg_to_buffer from Godot 4

[skadge]

Backported from 5786516d4d6b51

Rationale:
godotengine/godot-proposals#5059

[skadge]

Integration complete, but jpg encoding is ~grabbled. For instance, capturing a viewport's texture and saving it as a jpg:

get_node("Viewport").get_texture().get_data().save_jpg("/tmp/test.jpg", 0.9)

generates the following image:

If anyone knows what it might be (texture compression?), I'd love to hear. Otherwise I'll give it another go when I come back from holidays.

[skadge]

The code is now working as expected and ready for review.

[YuriSizov]

CI fails because you have formatting issues. Extra empty lines in the highlighted methods in cpp and wrong indentation in documentation XML.

[skadge]

@YuriSizov thanks, fixed. Let see if the CI is happy now.

[severin-lemaignan]

Any chance for that PR to be merged anytime soon?

[akien-mga]

Could you squash the commits? See PR workflow for instructions.

As a side note, it doesn't seem to be only a backport of #62122 as you seem to have also implemented the missing _jpeg_save_func. It would be good to point this out especially when it means that the master version was still broken. Thankfully it got reported as a bug and someone else has a PR implementing it: #66929.

[BlooRabbit]

Hello, is this going to be merged into 3.5 at some point ?

It is extremely useful to use jpg rather than png for saving in-game made images and optimizing save space (I have 1000nds of frog images to save 😁).

EDIT: Just tried it out myself, the commit works perfectly and the results are amazing in terms of space saving.